Which of the following statements is true?

a. a radius is always a chord.
b. a tangent is always a secant.
c. a diameter is always a chord.
d. a chord is always a diameter.

A isnt correct because radius goes from center of circle to any point on circle. Chord on the other hand connects 2 points on circle...

B is also false. Secant goes through circle while tangent only touches it in one point. 

C is correct. Chord connects as said before 2 points on circle and in some cases it can connect 2 points in such way that it goes through center which is diameter.

D is not correct because chord doesnt have to pass trought center of circle in order to connect any 2 points on circle.

Because it is the very esays way to learn